The present invention relates to a fluid dispenser or a fluid discharge device which includes a valve seat, a valve body biased rearward with respect to the valve seat and a push member disposed at the back of the valve body so that it moves forward against the biasing force to the valve body and opens a valve when a forward push force is applied thereto, the push member being disposed inside a shaft body so that the push force described above is applied indirectly to the push member through a fluid tank fitted removably to the push member. Here, examples of the fluid include writing fluids such as bokuju or China ink (black writing fluids), paint and ink, cosmetic fluids such as eye liner, lip color, and nail color, solutions such as seasoning, machine oil and cleanser, or suitable powder.
Japanese Utility Model Publication 63-19171/1988 discloses an example of the fluid discharge device of the kind described above. This publication shows a writing instrument of the type which operates a valve body by the push operation of a knock rod to supply ink in an ink storage portion toward a pen body or a nib of the instrument. A cylindrical member is fitted into a shaft cylinder neck portion, a valve seat is formed at the front open portion of the cylindrical member and the valve body is brought into pressure contact and engaged with the valve seat from the front by a spring member. A leg portion of the valve body is loosely fitted into a through-hole of the cylindrical member, and faces and comes into contact with the front end of an ink cartridge member fitted loosely into a rear shaft cylinder. A flexible cylinder member is interposed in an air-tight manner between the cylindrical member and the ink cartridge member to connect them together, and a small space for extension and contraction of the flexible cylindrical member is formed between the shaft cylinder and the ink cartridge member for the purpose of allowing forward and rearward movement of the ink cartridge member by the operation of the knock rod at the tail end of the shaft cylinder.
In the fluid discharge device having such a valve structure, which uses a fluid tank fitted removably to the push member, the following problems which are not encountered in those fluid discharge devices having no valve structure arise.
A first problem is leakage of the fluid.
When the fluid tank is fitted to and removed from the push member, turning force is often applied. As one can understand more easily by imagining the case of fitting and removing of the cartridge of a fountain pen, many users feel that the operation becomes easier by fitting or removing the cartridge while applying the force of "twist". Needless to say, this turning force does not in most cases cause any problem in the case of ordinary fountain pens. In the case of the valve structure described above, however, the application of the turning force to the fluid tank might result in the unnecessary leakage of the fluid.
A second problem is variance or unacceptable differences in the feel of operation of the device. When a plurality of products are produced, the feel of operation varies from product to product.
A third problem is defects in handleability.
These problems will be explained further with reference to the drive disclosed in the aforementioned publication (63-19171/1988).
If the turning force is applied to the main body of the ink cartridge when fitting and removing the main body of the ink cartridge to and from a convex reduced diameter member, this turning force is transmitted to the convex reduced diameter member. Accordingly, the convex reduced diameter member attempts to rotate but since a flexible cylindrical member is fitted to this convex reduced diameter member and this flexible cylindrical member is fitted to a cylindrical member fitted into the shaft cylinder neck portion, the turning force of the convex cylindrical member produces the twist of the flexible cylindrical member. It is true that the flexible cylindrical member may exhibit some flexibility and such a twist might not generate breakage, but the twist force applies an excessive force to the fitting portion with the flexible cylindrical member or to the fitting portion with the flexible cylindrical member or to the fitting portion with the cylindrical member. As a result, even if the flexible cylindrical member is not broken, the first problem of ink leakage often occurs from these fitting portions.
The structure wherein the leg portion of the valve body faces the front end of the ink cartridge causes the second problem in that when a plurality of products are produced, the feel of operation differs remarkably from product to product. In order for the leg portion of the valve body to face and come into contact with the front end of the ink cartridge member fitted to the flexible cylindrical member while the valve body is brought into pressure contact and engaged with the valve seat by the spring member, dimensional design must be made so that the flexible cylindrical member is brought into a tension state where at least a light tension is applied to the flexible cylindrical member by the spring member when no pushing force is applied. However, existing dimensional variance must be considered. Therefore, when a plurality of products are produced, variance occurs in this tension.
Furthermore, the third problem of inferior handleability occurs from the fact that the main body of the cartridge will tend to become detached from the convex reduced diameter member. In other words, when the main body of the cartridge is removed from the convex reduced diameter member, a tension is further applied to the flexible cylindrical member besides the tension described above, and this results in breakage of the flexible cylindrical member, and the like. In this case, "fitting" might permit "removability" and might prevent the above-mentioned breakage of the flexible cylindrical member with reference to the cylindrical shaft neck portion, the cylindrical member, the flexible cylindrical member, the ink cartridge member or the convex reduced diameter member. In this case, however, "fitting" must be accomplished once again during fitting and removal between the ink cartridge and the convex reduced diameter member and this becomes troublesome. If fitting and removal between the ink cartridge and the convex reduced diameter member can be carried out with little force, the flexible cylindrical member might not become broken, but the problem of ink leakage will become worse.